JP2008227337A - Near-field exposing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a near-field exposing method with which the pattern of a fine opening formed on an exposure mask can be accurately and efficiently exposed, with proximity EB lithography, to 1:1 with respect to an object to be exposed. <P>SOLUTION: The present invention relates to a near-field exposing method for exposing an object to be exposed using near-field light generated in the opening of an exposure mask comprising a light shielding film having the opening, including the steps of: when an opening width of the opening of the exposure mask is defined as s(nm), a working pitch of the object to be exposed is defined as p(nm) and coefficients are defined as (a) and (b), determining the opening width so as to satisfy an equation (1), inequality (2), and inequality (3); preparing the exposure mask including the opening with the opening width; and exposing the object to be exposed by irradiating the exposure mask with exposure light. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to a near-field exposure method, in particular, using an exposure mask provided with a light-shielding film having an opening smaller than the wavelength of light of an exposure light source,
The present invention relates to a near-field exposure method for exposing an object to be exposed by near-field light generated at an opening of an exposure mask by exposure light from an exposure light source.

In recent years, in the field of various electronic devices that require microfabrication such as semiconductor devices, there is an increasing demand for higher density and higher integration of devices. To meet these requirements, pattern miniaturization is required. It has become essential.
In recent years, projection system exposure apparatuses have become mainstream in order to satisfy these requirements.
A projection system exposure apparatus is generally composed of a light source, an illumination optical system, a mask on which a pattern is drawn, a projection optical system, and a stage for scanning an object to be exposed, and the resolution limit is about the wavelength of light.
For this reason, in order to increase the resolution, an immersion exposure technique has been proposed in which the projection optical system and the object to be exposed are filled with a liquid and exposed. However, the projection optical system is increased in size, accuracy, and complexity of the apparatus. There is also a problem that the cost of the apparatus increases due to the increase in the cost.

On the other hand, a near-field exposure method using near-field light generated from a minute opening formed in a light-shielding film on an exposure mask surface has been proposed as one of low-cost fine processing methods whose resolution does not depend on the wavelength of light. .
Since the intensity of near-field light generally attenuates rapidly with respect to the distance from the microscopic aperture, it is practically necessary for the object to be exposed and the microscopic aperture to be close to 100 nm or less. Further, it is known that the near-field light intensity in the vicinity of the minute aperture varies depending on the thickness of the light shielding film on the exposure mask surface, the pitch of the minute aperture, or the aperture width.
Therefore, it is important to control the near-field light distribution generated in the vicinity of the minute aperture by the size of the light shielding film and the minute aperture on the exposure mask surface in accurately exposing the pattern to the resist using the near-field light. .

In order to control such near-field light distribution, Japanese Patent Application Laid-Open No. 2004-228561 has conventionally proposed a method focusing on the thickness of the light shielding film on the exposure mask surface.
That is, according to this, the relationship between the thickness of the light shielding film, the aperture width of the minute opening, and the near-field light intensity is clarified, and the thickness of the light-shielding film is selected so as to obtain a desired near-field light intensity.
Non-Patent Document 1 reports that the thickness of the resist layer is optimized by focusing on the contrast of the near-field light distribution generated in the vicinity of the opening in the resist.
JP 2004-335752 A Applied Physics Letters 89, 031313 (2006)

However, in the above-described conventional example, the relationship between the intensity and contrast of the near-field light is clarified. However, the spatial distribution of the near-field light intensity, particularly the intensity gradient of the near-field light for 1: 1 exposure at 1: 1. Was not revealed.
In particular, how to make the spatial distribution of the near-field light intensity an important issue is to accurately and efficiently expose the resist with a minute aperture pattern formed on the exposure mask.

  In view of the above-mentioned problems, the present invention provides near-field exposure that enables a minute aperture pattern formed on an exposure mask to be exposed to an object to be exposed accurately and efficiently at 1: 1 magnification. It is intended to provide a method.

The present invention provides a near-field exposure method configured as follows.
The near-field exposure method of the present invention uses an exposure mask provided with a light-shielding film having an opening smaller than the wavelength of light of the exposure light source, and exposes the exposure mask with the exposure light from the exposure light source. A near-field exposure method for exposing an object to be exposed by generated near-field light,
When the opening width of the opening of the exposure mask is s (nm), the processing pitch of the object to be exposed is p (nm), and the coefficients are a and b, the following (Expression 1) and (Expression 2) And determining the opening width to satisfy (Equation 3);
Preparing the exposure mask having the opening with the opening width;
Irradiating the exposure mask with the exposure light and exposing the object to be exposed;
It is characterized by having.

In the near-field exposure method of the present invention, the object to be exposed is composed of a substrate having a high reflectivity with respect to the exposure light and a resist layer, and the thickness of the resist layer is not less than 120 nm and not more than 150 nm. It is characterized by that.
The near-field exposure method of the present invention is characterized in that the resist layer is constituted by a multilayer resist layer composed of at least an upper resist layer and a lower resist layer, and the thickness of the upper resist layer is 5 nm or more and 15 nm or less. To do.
The near-field exposure method of the present invention includes a development step in a subsequent step of exposing the object to be exposed.
After the development step, using the remaining upper resist layer as a mask, the base layer formed as the base of the upper resist layer is etched,
The lower resist layer is etched using the etched base layer as a mask.

  According to the present invention, a near-field exposure method capable of accurately and efficiently exposing a minute aperture pattern formed on an exposure mask to an object to be exposed 1: 1 in a 1: 1 magnification is realized. can do.

According to the near-field exposure method having the above-described configuration, it becomes possible to accurately and efficiently expose the pattern of the minute openings formed on the exposure mask to 1: 1 with respect to the object to be exposed. This is based on the following knowledge of the present inventors.
That is, the gradient of the near-field light intensity of the object to be exposed is maximized at a distance of 1/4 of the processing pitch from the opening center of the minute opening formed on the light shielding film of the exposure mask.
In the present invention, when the gradient of the near-field light intensity is maximized, the difference in dose (Dose amount) is maximized at the boundary between the exposed portion and the unexposed portion of the object to be exposed.
This has been found based on the knowledge that dose control is easy, and 1: 1 uniform exposure with high line width uniformity and high rectangularity is possible.

Below, the near-field exposure method in the Example of this invention is demonstrated.
FIG. 1 shows a flowchart for explaining the near-field exposure method of this embodiment.
FIG. 2 is a view for explaining an exposure mask used in the near-field exposure method of this embodiment.
In FIG. 2, 1 is a mask base material, 2 is a light shielding film, 3 is a minute opening pattern by an opening of an exposure mask, s (nm) is an opening width of an opening of the exposure mask, and p (nm) is an opening pattern. (The processing pitch of the object to be exposed).

In this embodiment, the wavelength of the exposure light is 365 nm. The exposure mask having the structure shown in FIG. 2 is used, and this exposure mask includes a light shielding film having an opening smaller than the wavelength of light of the exposure light source.
In the near-field exposure method of this embodiment, the object to be exposed is exposed by the near-field light generated at the opening of the exposure mask by the exposure light from the exposure light source in the following steps.
First, in step 1, when the processing pitch for processing the object to be exposed is p (nm) and the opening width of the minute opening pattern on the light shielding film of the photomask is s (nm), the following (formula A) is The opening width of the light shielding film provided on the exposure mask is determined so as to satisfy the condition.
Here, the processing pitch for processing the object to be exposed is the same as the pitch of the minute opening pattern.

s = 0.53p-8.3 (Formula A)

Next, in step 2, a photomask having the opening width determined in step 1 is manufactured.
In step 3, the photomask and the surface of the object to be exposed are brought into close contact with each other, and exposure light is irradiated to expose the object to be exposed.

Next, details of the near-field exposure performed by the present embodiment will be described with reference to FIG.
A photomask 4 is constituted by the mask base material 1, the light shielding film 2, and the minute opening pattern 3 for generating near-field light.
The pitch of the minute opening patterns 3 is the same as the desired processing pitch for processing the object to be exposed as described above, and is preferably about 200 nm or less.
The material of the mask base material 1 is silicon nitride, and the thickness thereof is about 500 nm.
The light shielding film 2 is made of amorphous silicon and has a thickness of about 50 nm.

Next, the exposure object used in the present embodiment will be described.
FIG. 3 shows a schematic configuration of an exposure object used in this embodiment.
The object to be exposed 9 is constituted by a multilayer structure composed of a multilayer resist layer composed of an upper resist layer 5, an SOG layer 6 and a lower resist layer 7, and a substrate 8.
The upper resist layer 5 is sensitized by the exposure wavelength and is patterned in the development process.
The thickness of each layer is approximately 10 nm for the upper resist layer 5, 20 nm for the SOG layer 6, 100 nm for the lower resist layer 7, and 500 μm for the substrate 8.
The upper resist layer 5 and the lower resist layer 7 are generally made of a resin material, and the material of the substrate 8 is silicon.

Next, an outline of the near-field exposure method in the present embodiment will be described.
FIG. 4 is a diagram for explaining the outline of near-field exposure in the present embodiment.
In the near-field exposure, the photomask 4 and the upper resist layer 5 to be exposed 9 are brought into close contact with each other, and then the exposure light is irradiated onto the photomask 4, and the upper resist is generated by the near-field light 10 generated in the vicinity of the minute aperture pattern 3. Layer 5 is exposed.
That is, a space where the intensity of near-field light is relatively high in the upper resist layer 5 is an exposed portion, and a space where the intensity is low is an unexposed portion.
At this time, it is known that the intensity of the near-field light 10 and its spatial distribution change in a complex manner depending on the pitch and opening width of the minute opening pattern 3 or the thickness and material of the layer structure of the object 9 to be exposed.
An electromagnetic field analysis method based on the FDTD method is known as a method for predicting the intensity of near-field light and its spatial distribution.

The present inventors applied the FDTD method to the near-field exposure shown in FIG. 4 and succeeded in predicting the intensity and spatial distribution of the near-field light 10.
FIG. 5 shows an example of near-field light intensity in the vicinity of the adhesion interface between the photomask 4 and the exposure object 9 in FIG. 4 obtained by the FDTD method.
For convenience, let Z be the direction perpendicular to the photomask 4 and X be the horizontal direction.
The isointensity line 14 indicates the spatial distribution of near-field light intensity.

Next, conditions for forming a 1: 1 fine concavo-convex pattern, for example, a line and space pattern, on the upper resist layer 5 of the object 9 to be exposed are shown.
Among the minute opening patterns 3, a position of a quarter of the pitch of the minute opening pattern 3 in the X direction from the opening center of one minute opening, and the boundary between the upper resist layer 5 and the SOG layer 6 of the object 9 to be exposed Attention is paid to the position in the Z direction corresponding to this.
The position shown above corresponds to the boundary between the exposed portion and the unexposed portion of the upper resist layer 5 in a 1: 1 line and space pattern.
When the intensity gradient in the X direction of near-field light at the boundary between the exposed portion and the unexposed portion in the upper resist layer 5 is the maximum, the difference in dose amount after irradiation with exposure light for a certain time becomes the maximum, and the 1: 1 line An and-space pattern can be obtained with high line width accuracy.

Next, FIG. 6 is a diagram for explaining the relationship between the opening width and the processing pitch at which the near-field light intensity gradient is maximized, in which the results obtained by the FDTD method are plotted.
FIG. 6 is a plot of the results obtained by the FDTD method.
FIG. 6 shows a microscopic aperture pattern 3 having a maximum intensity gradient of near-field light at the boundary between the exposed portion and the unexposed portion, where a desired processing pitch is p (nm) with respect to the object 9 to be exposed. When the opening width is s (nm), the one obtained by the above FDTD method is shown.
The processing pitch p and the opening width s obtained by the FDTD method can be approximated by a straight line with relatively high accuracy, and the relationship is s = 0.53p−8.3 as shown in the above (formula A). I found that I can express.
The above relationship does not depend on the thickness and material of the mask base material 1.

FIG. 7 is a diagram for explaining the relationship between the aperture width and the near-field light intensity gradient. FIG. 7 plots the near-field light intensity displacement per 1 nm in the X direction with respect to various aperture widths when the processing pitch is 44 nm. It is a thing.
According to the above (Equation A), when the processing pitch is 44 nm, the intensity gradient of the near-field light becomes maximum when the opening width is 15 nm, which coincides with the maximum value of the near-field light intensity displacement in FIG. .
Further, the maximum value of the near-field light intensity displacement per 1 nm in the X direction is 0.052, and the maximum value 80 as the near-field light intensity displacement per 1 nm in the X direction in the range of ± 5 nm with respect to the optimum aperture width of 15 nm. % Equal to 0.04 or more is obtained.
If it is approximately 80% or more of the maximum value of the near-field light intensity displacement, a 1: 1 line and space pattern can be obtained with high accuracy.
At this time, as in the above (formula A), the coefficient of the linear function is not limited to the intercept −8.3 with an inclination of 0.53, and the processing pitch p (nm) and the opening width s (nm) are as follows. The opening width may be determined so as to satisfy (Equation 1).
s = ap−b (Equation 1)
However, in order to obtain an intensity gradient corresponding to 80% or more of the maximum value of the near-field light intensity displacement, the coefficients a and b satisfy the following (Expression 2) and (Expression 3).

Next, details of each step shown in FIG. 1 will be described based on the relationship between the processing pitch obtained as described above and the opening width of the minute opening pattern 3 of the photomask 4.
In step 1, when the processing pitch p (nm) of the exposure object 9 is given, the opening width s (nm) of the minute opening pattern 3 of the photomask 4 is obtained by s = 0.53p−8.3.
Also, in step 2, a photomask 4 is provided that provides the minute opening pattern 3 having the opening width and processing pitch obtained in step 1 above.

Next, a manufacturing method of the membrane photomask in the present embodiment will be described.
FIG. 8 is a diagram for explaining a method for manufacturing a membrane photomask in the present embodiment.
First, a silicon nitride film 16 having a thickness of about 400 nm is prepared on both sides of the silicon substrate 15 (FIG. 8A).
Next, a back etch hole 17 is formed on the back surface of the silicon substrate (FIG. 8B).
Next, about 50 nm of amorphous silicon as the light shielding film 18 is formed on the substrate surface (FIG. 8C).
Next, the fine opening pattern 19 having the processing pitch and the opening width obtained in the step 1 is patterned on the light shielding film 18 with an electron beam drawing apparatus or the like ((d) of FIG. 8).
Next, by removing the silicon substrate 15 from the back etch hole 17 by anisotropic wet etching using KOH, the region where the micro-opening pattern 19 is patterned is thinned to form a membrane photo having the same structure as the photomask 4. A mask 20 is obtained (FIG. 8E).

Next, in Step 3 subsequent to Step 2, a method for adhering the membrane photomask and the upper resist layer will be described.
FIG. 9 is a view for explaining the state of contact exposure between the membrane photomask and the object to be exposed.
In step 3, the membrane photomask 20 prepared in step 2 and the upper resist layer 5 of the exposure object 9 are brought into close contact with each other.
The membrane photomask 20 is attached to a pressure vessel (not shown) and pressurized.
Since the area of the membrane photomask 20 that has been patterned by the applied pressure 21 is thinned, it can be in close contact with the upper resist layer 5 by bending.
After the contact, the membrane photomask 20 is irradiated with exposure light, and the upper resist layer 5 of the exposure object 9 is exposed with near-field light generated in the vicinity of the minute opening pattern 19.

Although the exposure process by the near-field exposure method of the present embodiment is as described above, the upper resist layer 5 is approximately 10 nm, and the thickness is insufficient for use in a wide range of industrial fields such as normal LSI manufacturing.
Therefore, the pattern formation process after exposure of the to-be-exposed object 9 for supplementing this will be described below.
Development processing is performed on the upper resist layer 5 after the near-field exposure. At this time, if the upper resist layer 5 is a positive resist, the exposed portion is removed in the developing step, and if it is a negative resist, the unexposed portion is removed in the developing step.
In this embodiment, a positive resist will be described.

FIG. 10 is a diagram for explaining a pattern forming method for an object to be exposed after exposure.
FIG. 10 shows a process of transferring a high aspect pattern.
In the present embodiment, a development step is included in the subsequent step of exposing the exposure object, and the upper resist layer 5 in the exposed portion is removed in the development step ((a) of FIG. 10).
Next, using the remaining upper resist layer 5 as a mask, the SOG layer 6 which is a base layer formed as a base of the upper resist layer 5 is etched using fluorine-based gas ((b) of FIG. 10).
Next, the lower resist layer 7 is etched using an oxygen-based gas using the etched SOG layer 6 as a mask.
In addition, the material of the lower resist layer 7 is a phenol resin that is resistant to a fluorine-based gas in a resin system ((c) of FIG. 10).

In order to apply the step of transferring the high aspect pattern shown in FIG. 10, it is desirable that the object to be exposed has a laminated structure of at least three layers on the substrate as shown in FIG. Although it is the structure of the to-be-exposed thing 9, the thickness of the upper resist layer 5 has preferable 10 nm, The said (Formula A) is effective even if it is the range of 5 nm-15 nm.
Since the thickness of the SOG layer 6 does not substantially affect the near-field light intensity and the spatial distribution in the upper resist layer, the selection range is wide but 20 nm is desirable for etching.
The thickness of the lower resist layer 7 is particularly preferably the sum of the thicknesses of the upper resist layer 5, the SOG layer 6, and the lower resist layer 7, that is, the thickness of the multilayer resist layer is 130 nm, but is preferably 120 nm or more and 150 nm or less. It is a range.

The reason is as follows.
Near-field light generated in the minute opening pattern 3 of the photomask 4 is converted into propagating light, and a traveling wave propagating through the upper resist layer 5 and the SOG layer 6 is generated.
Further, a traveling wave is reflected at the boundary between the substrate 8 and the lower resist layer 7 to generate a reflected wave, whereby a standing wave is generated in the multilayer resist layer.
When the upper resist layer 5 is about 10 nm thick and the multilayer resist layer is about 130 nm thick, a standing wave node is formed at the boundary between the upper resist layer 5 and the SOG layer 6.
This is because the reflectance of the substrate 8 with respect to the exposure light is low or the thickness of the upper resist layer 5 or the thickness of the upper resist layer 5, the SOG layer 6, and the lower resist layer 7 deviates greatly from the above range. The intensity of near-field light that exposes the upper resist layer 5 is enhanced.
For this reason, the substrate 8 is preferably made of a material having a high reflectance with respect to the exposure light. In this embodiment, the substrate 8 is made of silicon.

The results of quantitative investigation of the enhancement effect of near-field light intensity by standing waves in these multilayer resist layers are described below.
FIG. 11 is a diagram for explaining the relationship between the depth in the Z direction and the contrast.
In FIG. 11, when the processing pitch is 44 nm, the opening width is 15 nm, and the upper resist thickness is 130 nm, the position from the surface of the upper resist layer in the negative Z direction in FIG. It shows change.
Here, the contrast is an amount obtained by the following (Expression 4), where Imax is the maximum value of the near-field light intensity distribution in one cross section in the X direction at a certain position in the Z direction and Imin is the minimum value.

If the Z depth is within 15 nm, a contrast of 0.65 or more can be obtained, which is a sufficient condition for exposing the upper resist layer.
That is, sufficient exposure from the surface of the upper resist layer to 15 nm can be performed.
According to FIG. 11, the depth in the Z direction is preferably as small as possible. However, since the lower limit for applying the resist layer by spin coating or the like is about 5 nm, the thickness of the upper resist layer 5 is practically 5 nm or more and 15 nm or less. You can say that.

Next, FIG. 12 shows a diagram for explaining the relationship between the thickness of the resist layer and the contrast.
FIG. 12 shows changes in resist layer thickness and contrast at a depth of 10 nm in the Z direction when the processing pitch is 44 nm and the opening width is 15 nm.
The thickness of the resist layer optimum for contrast is 130 nm, but the thickness of the multilayer resist layer is preferably 120 nm or more and 150 nm or less because the above-described contrast of 0.65 or more is obtained.
Note that the multilayer resist structure of the object to be exposed 9 is desired when deep processing is required as in LSI manufacturing, and when the processing depth may be 10 nm or less, the object to be exposed is The structure which consists of a single layer resist layer and a board | substrate may be sufficient.
In this case, the thickness of the single resist layer is most preferably 130 nm, preferably 120 nm or more and 150 nm or less, and the substrate preferably has a high reflectance with respect to exposure light like silicon.

The flowchart for demonstrating the near-field exposure method in the Example of this invention. The figure for demonstrating the mask for exposure used for the near-field exposure method in the Example of this invention. The figure for demonstrating schematic structure of the to-be-exposed object used for the Example of this invention. The figure for demonstrating the outline | summary of the near field exposure in the Example of this invention. The figure for demonstrating an example of near field light intensity distribution of the vicinity of a minute opening pattern. The figure for demonstrating the relationship between the opening width | variety in which a near field light intensity gradient becomes the maximum, and a process pitch. The figure for demonstrating the relationship between opening width and a near-field light intensity gradient. The figure for demonstrating the manufacturing method of the membrane photomask in the Example of this invention. The figure for demonstrating the state of contact | adherence exposure of the membrane photomask and to-be-exposed object in the Example of this invention. The figure for demonstrating the pattern formation method of the to-be-exposed thing after exposure. The figure for demonstrating the relationship between Z direction depth and contrast. The figure for demonstrating the relationship between the thickness of a resist layer, and contrast.

Explanation of symbols

1: mask base material 2: light shielding film 3: microscopic aperture pattern 4: photomask 5: upper resist layer 6: SOG layer 7: lower resist layer 8: substrate 9: object to be exposed 10: near-field light 11: in FDTD method Photomask model 12: Micro-opening pattern model in FDTD method 13: Resist layer model in FDTD method 14: Concentration line 15 of near-field light intensity distribution 15: Silicon substrate 16: Silicon nitride film 17: Back etch hole 18: Light shielding film 19: Micro opening pattern 20: Membrane photomask 21: Pressure

Claims (4)

Using an exposure mask provided with a light-shielding film having an opening smaller than the wavelength of the light of the exposure light source, the object to be exposed by the near-field light generated in the opening of the exposure mask by the exposure light from the exposure light source A near-field exposure method for exposing
When the opening width of the opening of the exposure mask is s (nm), the processing pitch of the object to be exposed is p (nm), and the coefficients are a and b, the following (Expression 1) and (Expression 2) And determining the opening width to satisfy (Equation 3);
Preparing the exposure mask having the opening with the opening width;
Irradiating the exposure mask with the exposure light and exposing the object to be exposed;
A near-field exposure method comprising:

  The said to-be-exposed thing is comprised from the board | substrate with a high reflectance with respect to the said exposure light, and a resist layer, and the thickness of this resist layer shall be 120 nm or more and 150 nm or less. Near-field exposure method.   3. The near field according to claim 2, wherein the resist layer is composed of a multilayer resist layer including at least an upper resist layer and a lower resist layer, and the upper resist layer has a thickness of 5 nm to 15 nm. Exposure method. A development step is included in a subsequent step of exposing the object to be exposed,
After the development step, using the remaining upper resist layer as a mask, the base layer formed as the base of the upper resist layer is etched,
4. The near-field exposure method according to claim 3, wherein the lower resist layer is etched using the etched underlayer as a mask.

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